This type of footwear manufacturing process is described in the applicant's own PCT application, ES 2010/000108.
According to this application, the process entails cutting the pieces which will form the upper and preparing a mould and counter mould between which the volume required for both the upper and the sole of the footwear is calculated.
The mould comprises at least two parts in order to ensure that when these parts are separated, the mould remains open to allow the cut pieces which will form the upper to be introduced. The same applies to the counter mould, which will take on the form of the footwear last. Small ridges stick out from the inner surface of the mould, no higher up than the depth of the cut pieces which will form the upper. The ridges delimit the areas coinciding with the outline and position of the cut pieces in the formation of the footwear upper.
The cut pieces which will form the upper are then placed on the aforementioned areas, upside facing the mould, before the last is inserted and the mould is closed. The mould, last and cut pieces which will form the upper delimit a network of channels which lead to specific spaces between the mould and last, such as the space where the sole would be. A molten plastic material is then injected into the mould, which fills all the channels and spaces and comes into contact with the cut pieces which will form the upper in order to bind them together once it has cooled down.
Upon opening the mould, a seamless item of footwear is produced; all the cut pieces are separated by ridges corresponding to the path created by the aforementioned channels; these ridges serve to bind the cut pieces which form the upper together.
The process described is disadvantageous in that each mould can only be used to manufacture one footwear model, whose upper and position is formed by a fixed number of cut pieces. This makes the process more expensive given that a new mould is required for each footwear design.
With the process described, the use of a lining comprising one single cut piece is being considered; this lining would be a prefabricated kind of sock which would be applied to the last. This would make the manufacturing process more expensive and complicates the use of leather or non-stretch materials in the lining.